Turbine blade with increased film cooling

ABSTRACT

An air-cooled turbine blade having a plurality of serially spaced cavities therein is provided with cooling air inlets at its base. One of the inlets directs a cooling flow into a cavity proximate the trailing edge of the blade for cooling the blade surfaces defining this cavity. From this cavity, the flow is directed in serpentine fashion into a second cavity remote from the trailing edge for cooling the surfaces defining this latter cavity. The cooling flow is then directed in a film from the second cavity onto the outer surface of the blade for cooling the latter.

United States Patent 1 1 I 3,891,348 Auxier June 24, 1975 1 1 TURBINEBLADE WITH INCREASED FILM 3,560,107 2/1971 Helms 4l6/90 3,628,88512/1971 Sidenstick ct a1 416/97 COOLING Primary Examiner-Samuel FeinbergAttorney, Agent, or FirmDana F. Bigelow; Derek P. Lawrence [57] ABSTRACTAn aircooled turbine blade having a plurality of serially spacedcavities therein is provided with cooling air inlets at its base. One ofthe inlets directs a cooling flow into a cavity proximate the trailingedge of the blade for cooling the blade surfaces defining this cavity.From this cavity, the flow is directed in serpentine fashion into asecond cavity remote from the trailing edge for cooling the surfacesdefining this latter cavity. The cooling flow is then directed in a filmfrom the second cavity onto the outer surface of the blade for coolingthe latter.

7 Claims, 5 Drawing Figures TURBINE BLADE WITH INCREASED FILM COOLINGThe invention herein described was made in the course of or under acontract. or a subcontract thereunder. with the United States Departmentof the Air Force.

BACKGROUND OF THE INVENTlON This invention relates to blades for use inturbomachinery and. more particularly. to air-coolcd blades of theaforesaid variety.

In turbomachinery. a flow of pressurized working fluid is directed ontoa plurality of turbine blades mounted upon rotatable discs for impartingmomentum thereto. whereby the kinetic energy of the fluid flow may betransformed into torque. In a number of applications of turbomachineconcepts. and particularly with respect to turbojet engines, the workingfluid flow is heated to extremely high temperatures. and travels atextremely high velocities. As a result. it has become requisite todiscover ways in which to maintain the performance and reliability ofturbine blades subjected to such a working environment.

Improvements in metal alloys provided early solutions to thecontemporaneous problems of mechanical strength and heat resistance ofturbine blades. However. increased demands for performance and everlarger power outputs have mandated blade design variations in additionto improvements in material compositions. Objectives of the designvariations have been to provide means for passing cooling fluids to orthrough portions of the blades subjected to particular heating whilereinforcing the structure of turbine blades in the areas of particularmechanical stress.

Members of one variety of blades resulting from the application of thesecriteria have included a plurality of radially extending cavitiesserially spaced between the leading and trailing edges of the blades.The cavities perform the function ofdirecting a flow ofcooling fluidthrough the interior of the turbine blades in order to cool respectiveportions thereof. Cross ribs extending between adjacent cavities serveto increase the strength of the blades in the directions of stress towhich the blades are subjected. ln blades of this variety. it has beenthe conventional practice to provide cooling air inlets to the cavitieswhich open through the base or tip of each blade to passages in the discupon which the blades are mounted or to a plenum surrounding the disc.The cooling flow is passed from these inlets through the cavities andeventually is dumped out of the cavities through exits into theenvironment thereof for expulsion with the working fluid.

In modern. high-powered turbomachinery. overall operating efficiencysuffers when turbine blades are cooled by the inefficient application oflarge amounts of cooling air to the individual blades. since the workrequired to provide cooling air negates a similar amount of outputavailable from the engine. (onsequcntly. blades using minimum quantitiesof cooling fluid are desirable. Thus. it has become increasinglyimportant to make full cooling use of the cooling fluid passed througheach blade.

Variation of the flow path of the cooling fluid through the blades hasbeen suggested. whereby an increased portion of the available coolingpower of the fluid is utilized. A common approach has been to direct agiven cooling flow in a serpentine path serially through a number ofadjacent cavities prior to the expulsion thereof. It has been furthersuggested in the prior art to pass a flow of cooling fluid in thisserpentine fashion from the trailing edge cavity to one or more seriallyadjacent cavities before expelling the cooling fluid from apertures nearthe blade base. tip end and/or trailing edge. While the serpentine pathofthe fluid increases the utilization of available cooling power. thedumping of the used fluid from the tip. base end or trailing edge of theblade fails to comprehend further use to which the cooling fluid mightbe put. namely utilization of the fluids film cooling potential. Thispotential has in the past been utilized with respect to cooling flowintroduced into leading edge cavities. But the film cooling potentialremaining in trailing edge cooling flow upon completion of itsserpentine flow path has not been appreciated.

SUMMARY OF THE INVENTION It is therefore an object of the presentinvention to provide an air-cooled turbine blade having a pluralityofinternal cavities therein with means for further utilizing the coolingpotential of a flow of cooling air subsequent to the utilization of thisair for the cooling of the blade surfaces defining the internalcavities.

It is a further object of the present invention to accomplish thisincreased use of cooling potential by directing the flow of cooling airfrom an internal cavity onto the outer blade surface in a cooling film.

It is a more particular object of the present invention to perform thedirecting ofthe cooling air as a film onto the outer blade surface aftercompletion by the air of a serpentine flow path through seriallyadjacent internal cavities originating with the trailing edge cavity.

The present invention seeks to more fully utilize the cooling power ofthe quantity of cooling fluid supplied to turbine blade trailing edgecavities by expelling particular portions ofthat fluid (which otherwisewould be dumped into the gas stream) in a film onto the outer surface ofthe blade. In order to accomplish this. the present invention provides anumber of exit apertures communicating the outer blade surface to theinterior of a particular blade cavity. This cavity is the one which thecooling flow reaches upon completion of a predetermined flow paththrough the blade. The apertures are arranged in a manner appropriate tothe formation of a cooling film upon the blades outer surface. Theresulting fluid film serves to convectively remove heat from thissurface as well as to form a barrier against direct impingement upon theblade by the hot working fluid. As a result. the external blade surfacetemperature remains lower. so that less cooling air need be provided.Consequently. the overall efficiency of the engine is enhanced.

Further objects of the present invention will become apparent from thedetailed description of a preferred embodimentcontained hereinafter asillustrated by the following figures wherein:

FIG. I is a section view of a typical turbojet engine showing theessential elements thereof;

FIG. 2 is a partial section view of the turbojet engine of FIG. 1showing the turbine arrangement in greater detail;

FIG. 3 is a section view of the blade of FIG. 2 taken along lines 3-3;

FIG. 4 is a half-section view of the turbine blade of the presentinvention; and

FIG. 5 is a schematic diagram ofthe flowpath ofcooling air within theturbine blade of FIG. 2.

DESCRIPTION OF A PREFERRED EMBODIMENT The following descriptionamplifies the particular embodiment of the present invention depicted inthe accompanying drawings. ()ne skilled in the art might easilyrecognize numerous changes which may be made in the structure of thisembodiment without departing from the spirit of the present invention.

The turbojet engine depicted in FIG. I comprises the basic elements oftypical machinery of this variety. A substantially cylindrical housingsurrounds a compressor I0. combustors I]. and a turbine 12, all disposedabout rotatable shaft 13. As is well known in the art. atmospheric airenters the machine from the left to be pressurized. heated and expelledto the right to provide usable thrust. More particularly. air entersfrom the left and is operated upon by the compressor (in combi nationwith the shape of the lead end of shaft 13) to be pressurized anddirected. in part. into combustors 11. Heat energy is added to the airwithin the combustors by the burning of appropriate fuel suppliedthereto. Working fluid. which is a combination of air and burned fuel.exits at the right end of the combustors and impinges the pluralityofturbine blades 14 carried by a number of adjacent discs making up theturbine l2. The impingement of the turbine blades 14 by the workingfluid serves to drive the turbine in rotation. which rotation isimparted to shaft l3. The rotation of shaft 13 is the motivating forcefor the operation of the compressor 10 at the forward end of themachine.

Turbine blades 14 must be extremely strong and heat resistant in orderto withstand the force and heat of the impinging working fluid. Thecooling system of the present invention. by which the blades l4 areprotected from overheating. is depicted in H05. 2 through 5 and operatesby making use ofa portion of the air operated upon by compressor 10 butnot directed into the combustors 1].

H6. 2 shows a typical turbine blade 14 and its cooperation with shaft 13and elements of the cooling system which are elucidated hereinafter.Blade 14 includes a blade shell [6 in the shape of an airfoil, and aplatform [8 adapted to cooperate with disc 19 by which the plurality ofblades are supported. Blade shell 16 has an outer surface 17 and aplurality ofinner cavities which will also be discussed hereinafter. Atthe blade tip (the blade end opposite platform 18) is a closure 20 whichseparates the blade inner cavities from environmental atmosphere. andwhich may be integral with the blade shell 16 or a separate pieceaffixed thereto. The blade shell l6 further has a leading edge 26 and atrailing edge 28.

In the embodiment ofthe invention disclosed in FIG. 2, an aperture 22 inshaft [3 permits the passage therethrough of cooling air from a coolingair expander 24 cooperating with an appropriate plenum (not shown) forthe delivery of cooling air to the blade. It is recognized that thepresent invention is equally applicable to blades which are designed tobe cooled by the application of air provided through inlets located nearthe tip of the blade rather than near the platform or by internalturbine circuits that do not use a cooling air expander. The presentembodiment is to serve only as an example and not be considered the onlyembodiment of the present in ention.

The cross-sectional viewsof blade [4 depicted in HUS. 3 and 4. takentogether with the schematic flow path of Fl(]. 5. disclose the bladestructure which directs the application ofthe cooling air fed to theblade platform 18 as described above. FIGS. 3 and 4 show that theturbine blade ofthe present embodiment of the invention incorporatesfirst. second and third cavities labeled 30. 32 and 34. respectively.which are disposed serially adjacent to one another between leading edge26 and trailing edge 28 of the blade shell lb. The cavities are definedwithin the shell by inner shell surfaces 3|. 33 and 35. respectively.The three cavities are of shape and size determined to be appropriatefor the optimization of cooling efficiency and mechanical bladestrength. Cavity 30 is disposed proximate trailing edge 28 of the blade.while cavity 32 is disposed remote from the trailing edge 28. Cavity 34is disposed proximate the leading edge of the blade.

lnserts 36 and 38 are disposed respectively within cavities 32 and 34.and respectively bear pluralities of orifices 37 and 39 for thedistribution of cooling air in an impinging flow against the innersurfaces of each respective cavity. The inner surfaces 3| of cavity 30are provided with a plurality of protrusions 31a appropriatelypositioned to enhance the turbulence of flow for minimum pressure drop.As defined by the state of the art. the impinging flow associated withcavities 32 and 34 and the turbulent flow associated with cavity 30 aresuperior in cooling characteristics to the flows which would occurwithin the cavities absent the provisions described.

The blade 14 of the present embodiment is provided with two inlets 40and 42 for the entry of cooling fluid from passage 22 (see FIG. 2). Itis noted that the two inlets 40 and 42 service cavities 30 and 34,respectively. Means for passing cooling fluid to cavity 32 in' eludes apassage 44 between cavities 32 and 30 disposed in proximity to the tipof blade 14 and remote from inlet 40. The two cavities 30 and 32 andpassage 44 define a serpentine path for the cooling fluid entering inlet40.

The definition of appropriate exits for the cooling fluid. which exitscombine with the foregoing blade structure to maximize the utilizationof the cooling fluid. accomplishes the objects of the present invention.As in the prior art. a minor portion of the cooling fluid which has beenintroduced through trailing edge inlet 40 is exhausted through aplurality of exit apertures 46 provided at the trailing edge 28 of theblade shell 16. As is also prevalent in the prior art. a portion of theair entering leading edge cavity 34 through inlet 42 is exhaustedthrough three groups of exit apertures 48. 50 and 52 positioned andadapted to direct the exit ing fluid in a film across various portionsof the outer surface of the blade shell in.

Film cooling has been found to be useful to increase the use to whichcooling air may be put. whose cooling potential has not been exhaustedduring application to the inner surfaces of the blade shell. lf. afterpassing from the inlet 42 and through orifices 39 in insert 38 andagainst surfaces 35. the air within cavity 34 re mains at a temperaturelower than that existing in the working fluid near the outer surfaces ofthe blade shell 16. the passing of this air out of cavity 34 in a filmacross such outer surfaces would serve to cool them and thus to makefurther use of the cooling flow. it is precisely to this film-coolingconcept that the present invention is directed While the prior art hascomprehended the use of exit film cooling to maximive the utili/ation ofthe cooling power of air fed into leading edge cavities. it has beencommon practice with respect to cooling flow fed into trailing edgecavities to dump the flow out of exit apertures at the tip. base ortrailing edge of the blade after an internal serpentine path has beencompleted. Wherever the working fluid near the outer surfaces of theblade to which this latter flovv might be directed is at a temperaturehigher than the exiting cooling flow. this practice constitutes a wasteof cooling power.

The present invention thus provides a plurality of spaced exit apertures54 through which the cooling fluid may be directed onto the outersurface of blade shell l6 downstream of apertures 54. Apertures 54 arelocated substantially along a radial line between the ends of bladeshell 16 and are configured appropriately for the formation of a coolingfilm upon the outer blade surface. The film thus formed serves as abarrier to protect the blade from the direct impingement of the hotworking fluid. Further. the film serves to remove heat from the bladesurface by convective heat flow. This added usage of the cooling powerof the cooling fluid allows the turbine blade to be cooled to the sameextent as previously. but with the expenditure of less cooling fluid. Asdescribed above. beneficial effects upon the overall efficiency of theturbomachine are thus achieved.

The operation of the cooling system of the present invention will now bedescribed with the aid of the alphabetical designations of locationsdepicted in FIGS. 3 and 4 and represented schematically in FIG. 5.Cooling air from the plenum is passed through air passage 22 of FIG. 2to the platform 18 of blade l4 and into inlets 40 and 42 of FIG. 4. Thatportion of the flow entering inlet 42 passes from point A below cavity34 to point B within cavity 34 and into contact with insert 38. The airis passed through orifices 39 and into the area represented by point C.which is defined by the insert 38 and inner surfaces 35 of the bladeshell. The impingement of this air against surfaces 35 serves to coolthese surfaces before the air is exhausted through exit apertures 48 andSt) to points D and E. respectively. The working fluid flowing pastpoints D and E impinges the exiting cooling fluid and. due to theviscous forces therehetween. creates films to the downstream sides ofeach point which films serve to cool the external surfaces of the bladeshell [6 until the films are separated therefrom by turbulence.

The second portion of cooling air flowing into the blade (through inlet40) passes from point F below the blade shell to point (i proximate theblade tip closure 20. Since the flow enters the blade at the trailingedge at its coolest temperature. a minimum portion of this fluid isforced out of cavity 30 through trailing edge exit apertures 46. Thepredominant portion of the fluid passes through passage 44 from point 0to point H within cavity 32. This flow continues past point I withincavity 32 and to point J. While within cavity 30, the cooling fluid actsin turbulent flow to cool surfaces 3!. Having passed into cavity 32. thefluid is directed by orifices 37 of insert 36 into the area representedby point K and into impingement with surfaces 33 for the coolingthereof. Having progressed to this point and having htl been raised intemperature by contact with surfaces 3] and 33 of the blade shell. thecooling fluid remains at a temperature below the external surfacetemperature of the blade shell. Thus. the fluid still possesses usablecooling power. Accordingly. there are provided apertures 54 throughwhich the fluid is subsequently passed to point l. outside of the bladeshell. The viscous forces of the passing working fluid act upon theexiting cooling fluid to create a cooling fllm downstream ofexitorifices 54 upon the outer surface of the blade shell proxi matetrailing edge 28. This film forms a barrier between the outer bladesurface and the working fluid. The film also cools the blade surface byconvective heat transfer. Consequently. the film serves to further coolthe blade by increasing heat transfer to the cooling fluid after itsexit from the blade.

In this way. the present invention increases the utilization of thecooling power ofa given quantity of cooling fluid by maximizing thecontact with various turbine blade shell surfaces of that portion of thecooling fluid fed into trailing edge cavities. Were the fluid enteringinlet 40 to be dumped into the passing working fluid from either the tipor base ends of the blade shell, no film would be created upon the outersurface of the blade by this fluid. and the remaining cooling powerthereof would be wasted. By the application of the present invention toturbine blades. reductions in the amount of cooling fluid required to befed to the rear or trailing edge blade cavities may be effected. withattendant increases in machine efficiency.

While the present invention has been described in conjunction with apreferred embodiment thereof. it is apparent that numerous variations inthe application thereof may be made without departing from the spirit ofthe invention. For example. a turbine blade having a plurality ofcavities in a number of larger than the three disclosed might be devisedwherein cooling air fed to one of the cavities proximate the trailingedge is passed in a serpentine path through serially adjacent cavitiesand finally exhausted in a cooling film upon external blade surfaces.Another variation, which was discussed briefly above. might involve theapplication of cooling fluid through inlets located near the tip ratherthan the platform of the blade shell. Additionally. while the embodimentherein disclosed passes a cooling film over only one side of the outersurface of the blade shell. a plurality of apertures could easily beapplied which would serve to communicate the other side of the shell toa trailing edge cavity for the passing of cooling fluid thercacross.

Other modifications of the described embodiment of the invention willoccur to those skilled in the art within the scope of the presentinventive concept without departing from the spirit thereof.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

I. In a turbomachine. an air-cooled blade comprising:

a blade shell having an outer surface. first. second and third innersurfaces. and a leading edge and a trailing edge;

a first cavity in said shell proximate said trailing edge and formed bysaid first inner surface of said shell.

a second cavity in said shell remote from said trailing edge and formedby said second inner surface of said shell;

a third cavity in said shell proximate said leading edge and formed bysaid third inner surface of said shell;

means for introducing cooling air into said first cavity for coolingsaid first inner surface:

means for introducing cooling air into said third cavity for coolingsaid third inner surface:

a plurality of passageways formed through said trail ing edge andcommunicating with said first cavity for efflux of a first portion ofsaid first cavity cooling air therefrom;

means for directing the remainder of said first cavity cooling air fromsaid first cavity into said second cavity for cooling said second innersurface: and

means for directing all of said cooling air delivered to said secondcavity in a film from said second cavity onto said outer surface forcooling said outer surfacev 2. The blade of claim I further comprisingfirst and second blade ends and a pair of ribs located internally ofsaid shell and extending between said first and second blade ends.wherein said means for introducing cooling air into said first cavity isdisposed proximate said first blade end. and said means for directingsaid cooling air into said second cavity comprises an opening in one ofsaid ribs disposed proximate said second blade end.

3. The blade of claim I further comprising a radially outward tip endand a radially inward platform wherein said means for directing saidcooling air onto said outer surface comprises a plurality of spacedapertures providing communication between said second cavity and saidouter surface. disposed between said tip end and said platform andsubstantially aligned along a radial line along said blade shell.

4. The blade of claim 3 further including a hollow impingement insertpositioned within said second cavity. and said cooling air directingmeans directs said remainder of said cooling air initially to theinterior of said insert.

5. The blade of claim 4 further including a second hollow impingementinsert positioned within said third cavity.

6. An air-cooled blade for use in a turbomachinc.

said blade comprising;

a blade shell in the shape of an airfoil having a leading edge and atrailing edge and further having an outer surface and first. second andthird inner surfaces and first and second ends;

a blade platform proximate the first end of said shell;

first. second and third serially spaced cavities defined respectively bysaid first. second and third inner surfaces of said shell and disposedrespectively proximate said trailing edge. remote from said trailingedge. and proximate said leading edge;

a blade closure proximate the second end of said shell for separatingsaid cavities from an environmental atmosphere:

means for introducing a first flow of cooling air through said platforminto said first cavity for cooling said first inner surface;

a plurality of passageways formed through said trailing edge andcommunicating with said first cavity for efflux of a first portion ofsaid first cavity cooling air therefrom.

means proximate said closure for directing the remainder of said firstflow from said first cavity into said second cavity for cooling saidsecond inner surface;

means for directing all of said first flow delivered to said secondcavity in a film from said second cavity onto said outer surface forcooling said outer surface:

means for introducing a second flow of cooling air through said platforminto said third cavity for cooling said third inner surface; and

means for directing said second flow in a film from said third cavityonto said outer surface for further cooling said outer surface. l

7. The blade of claim 6 wherein said means for directing said first flowonto said outer surface comprises a plurality of spaced aperturessubstantially aligned along a radial line between said first and secondends of said blade shell.

1. In a turbomachine, an air-cooled blade comprising: a blade shellhaving an outer surface, first, second and third inner surfaces, and aleading edge and a trailing edge; a first cavity in said shell proximatesaid trailing edge and formed by said first inner surface of said shell;a second cavity in said shell remote from said trailing edge and formedby said second inner surface of said shell; a third cavity in said shellproximate said leading edge and formed by said third inner surface ofsaid shell; means for introducing cooling air into said first cavity forcooling said first inner surface; means for introducing cooling air intosaid third cavity for cooling said third inner surface; a plurality ofpassageways formed through said trailing edge and communicating withsaid first cavity for efflux of a first portion of said first cavitycooling air therefrom; means for directing the remainder of said firstcavity cooling air from said first cavity into said second cavity forcooling said second inner surface; and means for directing all of saidcooling air delivered to said second cavity in a film from said secondcavity onto said outer surface for cooling said outer surface.
 2. Theblade of claim 1 further comprising first and second blade ends and apair of ribs located internally of said shell and extending between saidfirst and second blade ends, wherein said means for introducing coolingair into said first cavity is disposed proximate said first blade end,and said means for directing said cooling air into said second cavitycomprises an opening in one of said ribs disposed proximate said secondblade end.
 3. The blade of claim 1 further comprising a radially outwardtip end and a radially inward platform wherein said means for directingsaid cooling air onto said outer surface comprises a plurality of spacedapertures providing communication between said second cavity and saidouter surface, disposed between said tip end and said platform andsubstantially aligned along a radial line along said blade shell.
 4. Theblade of claim 3 further including a hollow impingement insertpositioned within said second cavity, and said cooling air directingmeans directs said remainder of said cooling air initially to theinterior of said insert.
 5. The blade of claim 4 further including asecond hollow impingement insert positioned within said third cavity. 6.An air-cooled blade for use in a turbomachine, said blade comprising: ablade shell in the shape of an airfoil having a leading edge and atrailing edge and further having an outer surface and first, second andthird innEr surfaces and first and second ends; a blade platformproximate the first end of said shell; first, second and third seriallyspaced cavities defined respectively by said first, second and thirdinner surfaces of said shell and disposed respectively proximate saidtrailing edge, remote from said trailing edge, and proximate saidleading edge; a blade closure proximate the second end of said shell forseparating said cavities from an environmental atmosphere; means forintroducing a first flow of cooling air through said platform into saidfirst cavity for cooling said first inner surface; a plurality ofpassageways formed through said trailing edge and communicating withsaid first cavity for efflux of a first portion of said first cavitycooling air therefrom, means proximate said closure for directing theremainder of said first flow from said first cavity into said secondcavity for cooling said second inner surface; means for directing all ofsaid first flow delivered to said second cavity in a film from saidsecond cavity onto said outer surface for cooling said outer surface;means for introducing a second flow of cooling air through said platforminto said third cavity for cooling said third inner surface; and meansfor directing said second flow in a film from said third cavity ontosaid outer surface for further cooling said outer surface.
 7. The bladeof claim 6 wherein said means for directing said first flow onto saidouter surface comprises a plurality of spaced apertures substantiallyaligned along a radial line between said first and second ends of saidblade shell.